It has traditionally been the case that a telephone customer has a single twisted pair connection to a central office of a local telecommunications company through which local and long distance service is provided. It has also become standard practice to allow long distance carriers access to a customer after the local switch, so that long distance calls are routed from a switch of the local telecommunications company to the long distance carrier's network. In recent years, the local telecommunication company has provided various services such as Call Waiting, Call Transfer, etc. that supplement the switching a calls to and from a called subscriber. Call Waiting is a service where a predetermined Call Waiting Tone is provided to a subscriber when a second call is received for a same subscriber number (or line on the switch of the local telecommunication company) when the subscriber is already busy on a first call. In response to the Call Waiting Tone, the subscriber has the option of transferring from the first call to the second call while the central office of the local company places the first call on hold. After answering the second call, the subscriber can transfer back to the first call by generating a Flash Hook signal with the Telephone Set to finish that call.
U.S. Pat. No. 4,852,153 (Streck), issued on Jul. 25, 1989, discloses a telephone/facsimile system including a plurality of telephones and a facsimile device connected to a common telephone line. The incoming calls are automatically switched from the telephones to the facsimile device as appropriately needed. Still further, the common telephone line is used for both incoming and outgoing calls by the telephones and the facsimile device, and is transparent to users. More particularly, a telephone cable enters a house or small business and is connected to a plurality of outlets to which the telephones are separately connected. One of the outlets is coupled to a master telephone which comprises switching means for separately connected a telephone and a facsimile device to the telephone line.
Various arrangements such as a Private Branch Exchange (PBX) are also known for connecting a telephone or data terminal to two telecommunication networks. More particularly, it is probable that a customer or subscriber will have both regular and alternate local access connections in the near future, implying that an additional twisted pair connection will be provided to the customer or subscriber location. This alternate connection may originate from a central location (e.g., an alternate central office), but is more likely to originate from a location remote from the alternate central office. The remote location can be, for example, an Optical Network Unit (ONU) connected via an optical fiber to a Host Digital Terminal (HDT) which is resident in, or connected to, the alternate central office, or a Coaxial network Unit (CNU) which is connected to a Host Digital Terminal (HDT) via a fiber/coaxial network (e.g., a cable television network) that is presently used to provide broadcast television programming. In either case, the subscriber is provided with two twisted pair connections. A simple solution to connecting the first and second twisted pair connections (lines) at the subscriber location is to have a first and second telephone sets (station sets) dedicated to each of the first and second lines, respectively. This is inconvenient since the subscriber generally has a number of station sets which are distributed throughout the subscriber's residence or location. Therefore, dedicating only one of these station sets for access to the alternate connection (e.g., alternate central office) does not allow for answering or originating calls on the alternate connection except from one specific location in the residence or location.
U.S. Pat. No. 4,803,360 (Morstadt), issued on Apr. 9, 1974, discloses switching apparatus permitting automatic call answering by a single data terminal having access to two telecommunication networks, or automatic call origination by the data terminal on either of the two networks. More particularly, the data terminal has access to the two telecommunication lines to automatically answer a line carrying an incoming call while excluding the other line. Still further, the data terminal manually or programmably selectively accesses one of the two telecommunication lines in accordance with data information to be transmitted to the selected telecommunication line for automatic call origination. However, when the call is answered or originated, the apparatus causes a change in the central office coupled to the telecommunication line used. For example, when a telephone call is automatically answered, a signal is sent back to the central office to cause various reactions to occur such as a disconnecting of ringing tone, etc.
It is desirable to provide apparatus which is connected to at least two telecommunication lines on one side and to a telecommunications device on the other side, which is powered from one or more of the telecommunication lines, and which automatically switches an incoming call on either of the two lines to a station device without consideration of answering the incoming call. Still further, it is desirable that the apparatus automatically switches a call originated at the station device to a desired one of the telecommunication lines. In either direction, it is desirable that the apparatus be transparent to the station device and the telecommunication lines so as not to affect the operation of either the station device or the central offices connected to the telecommunication lines. Additionally, the apparatus should advise the subscriber of an incoming call on a second line when a first line is in use without causing a busy signal to be returned on the second line, and allow the subscriber to switch from one line to the other upon receipt of a second concurrent call without losing the first call.